Project II focuses on obesity among the children of Mexican immigrants ages 5-14. Mexican-origin boys in immigrant families have particularly high obesity rates relative to all other children, including Hispanic boys in native families. The proposed research will examine how immigration to the United Statesand family, school, and neighborhood contexts within the United Statesindependently and jointly influence the risk of obesity among children of Mexican immigrants. The research will emphasize two aspects of children's contexts: the level of economic disadvantage and the degree to which they expose children to the wider American society beyond the Mexican community. These factors represent important dimensions of assimilation (cultural and economic) and are theorized to shape children's environments in complex ways that raise and lower the risk of obesity. An innovative component of the proposed research is its consideration of how the migration process itself affects children's weight. The research will go far beyond prior research on children's weight by comparing children living in Mexico with children of Mexican immigrants living in the United States, and by using propensity scores to compare children of Mexican immigrants with children living in Mexico whose parents have a high propensity to migrate. Another innovation is that the project will assess the role of parental legal status on children's weight using data from the NHIS-OIS. Finally, a third innovation is that the research will unpack the concepts of acculturation and SES into components that are likely to reduce resistance to obesity and components that are likely to increase exposure to the risk of obesity. The research team will examine how these are independently and jointly related to children's weight. For example, we hypothesize that one aspect of low acculturationbeing socialized in Mexicois associated with having heavier children. But we expect another aspect of low acculturationsocial isolation from the U.S. mainstreamto have the opposite effect because it reduces exposure to the U.S. obesiogenic environment.